The present invention relates to a hybrid aircraft, and more particularly, to directing cooling air flow from an inlet to an exhaust within a rotor duct of a hybrid unmanned aerial vehicle (UAV).
There is an increased emphasis on the use of UAVs for performing various activities in both civilian and military situations where the use of manned flight vehicles may not be appropriate. Such missions include surveillance, reconnaissance, target acquisition, target designation, data acquisition, communications relay, decoy, jamming, harassment, ordinance delivery, or supply.
A hybrid aircraft provides the hover and low-speed maneuverability of a helicopter with the high-speed forward flight and duration capabilities of a winged aircraft. Capability for such flight modes creates complications for a cooling system which must always provide adequate air-cooling flow to a vehicle engine. Providing adequate air-cooling flow is further complicated as the engine is typically buried within the vehicle body. In one conventional cooling system a cooling fan or xe2x80x9cblowerxe2x80x9d arrangement provides substantial airflow over the engine irrespective of the aircraft""s flight mode. Disadvantageously, providing adequate cooling-air flow in all hybrid aircraft flight modes requires a cooling system which may be rather heavy and complicated.
Accordingly, it is desirable to provide a cooing system for a hybrid aircraft which is lightweight, uncomplicated and provides adequate cooling air flow in all flight modes.
A cooling system for a hybrid aircraft according to the present invention includes an inlet in the body and an exhaust within a rotor duct. An air-cooling flow path for an air-cooling system is thereby provided from the inlet, over a powerplant subsystem and into the rotor duct through the exhaust.
A cooling fan is located adjacent the inlet to supplement the air-cooling flow from the inlet. The cooling fan is integrated with an engine flywheel to minimize packaging space, size and weight.
In a hover mode, there is a significant low-pressure area created inside the rotor duct by a rotor system. The low-pressure area within the rotor duct assists in drawing air through the inlet and over an engine via the exhaust. The low-pressure area within the rotor duct provides a portion of the necessary air-cooling flow over the engine. The cooling fan need only supplement the air-cooling flow. A more compact and lighter system is thereby provided. In addition, a greater percentage of power from the engine is available to the rotor system.
In a transition mode, the low-pressure area created inside the rotor duct decreases. Ram air pressure through the inlet, however, increases due to the increase forward flight speed. The net air-cooling flow is approximately the same as in hover mode.
In a forward flight mode, the pressure inside the rotor duct is near atmospheric and there is no air-flow draw through the exhaust. However, ram air through the inlet is substantially increased due to the forward flight speed. Moreover, the ram air pressure through the inlet creates a pressure differential between the inlet and exhaust to assure a continuous air-cooling flow over the engine.
A muffler is also exhausted directly through the exhaust to minimize openings in the vehicle body. By diffusing the heated exhaust from the muffler into the rotor duct, the heat signature of the hybrid aircraft is advantageously reduced.
The present invention therefore provides a cooling system for a hybrid aircraft which is light weight, uncomplicated and provides adequate cooling air flow in all flight modes.